A further evaluation of some polyurethane elastomers as maxillofacial prosthetic materials will be conducted. The major efforts will be focused on: 1. a further study of efficiency of various kinds of plasticizers in the Calthane ND2300 system and hopefully an ideal plasticizer will be chosen for further improvement of the system than the current one used, Benzoflex-9-88; 2. to determine the toxicity of Calthane ND2300 plasticizer system through skin irritation tests; 3. to achieve the best balance of properties of Calthane NF310 W through the introduction of plasticizers; 4. to obtain quantitative data on the UV resistance of isophorone-polymeg system in the presence of UV stabilizers; 5. to determine the migration of the promising UV stabilizers used in isophorone-polymeg system under normal cleaning conditions and its degree of irritation ot the skin; 6. to locate additional new polyurethanes from the market during the research period and conducting preliminary study of these materials for maxillofacial applications; 7. to continue the investigation of custom-synthesized polyurethanes through the incorporation of different kinds of basic raw materials; and 8. to develop suitable methods to improve the U-10-X4D urethane elastomers with emphasis on tensile strength. Through these achievements materials which are better than those now available will be formulated for clinical test.